The cpu frequency scaling monitor shows that my 2.6GHz cpu is running at 1200MHz. Even changing the governor from ondemand to performance doesn't change this.

This may have started with a few kernel mods to be able to use powertop. I enabled CONFIG_NO_HZ, CONFIG_CPU_IDLE_GOV_MENU, and CONFIG_TIMER_STATS. These are literally the only additions to a kernel that was working fine.

Let me boot into the kernel I installed in November and re-emerge a few packages.

And now, the solution. Technically, it's off-topic for this forum, but it's a solution.

I played with various of my historical kernels and the cpu frequency was stuck to 1.2GHz, no matter what. Booted sysresccd off USB and found the same. Booted into FreeBSD, and here, cpu frequency scaled fine.

With help of my search engine of choice, I finally found this: http://www.thinkwiki.org/wiki/Problem_with_CPU_frequency_scaling, and the pieces clicked into place. For a few weeks, I've been using another Lenovo laptop's charger, as it turns out, a 65W model (presumably - it doesn't say so explicitly, but 20V at 3.25A is a pretty close match in my book). Going back to the 90W charger fixed my problem.

For the record, this is a T530. While not explicitly listed at above URL, it strongly matches the "it is probably true of all Lenovo ThinkPads" statement.